Increased [68Ga]Ga-SST uptake in the uncinate pancreatic process in new digital PET/CT machine and potential association with clinical and histologic factors in NET patients.

Introduction: A physiological increase in the uptake of [⁶⁸Ga]Ga-labeled somatostatin analogues ([⁶⁸Ga]Ga-SST) PET tracers has been reported in the uncinate pancreatic process (UP) and might be even higher in latest generation of PET/CT scanners and might be falsely interpreted as NET. We aimed to investigate the uptake of UP in a large population of NET patients who underwent [⁶⁸Ga]Ga-SST PET/CT with digital SiPM detectors. We also explored potential associations between UP uptake and various clinical, imaging, and pathological factors routinely assessed in NET patients.

Methods: We analyzed all consecutive NET patients from July 2018 to June 2022 in this retrospective, single-center study. All patients underwent a [⁶⁸Ga]Ga-SST PET/CT scan on a digital SiPM PET/CT scanner. On visual analysis, we distinguished between normal linear and homogenous UP uptake or abnormal if otherwise. We compared SUV_max/mean in patients with normal UP uptake to those with abnormal UP uptake with suspicious NET lesions on contrast-enhanced CT (ce-CT) and according to the site of the primary NET (pancreatic NET vs. other), patient gender (female vs. male) and tumor grade (grade 1-2 vs. 3) using a Mann-Whitney test. We also assessed the correlation between SUV_max/mean values in UP with patients' age, primary NET Ki-67 counting, and its SUV_max/mean, TLA and MTV values.

Results: We included 131 NET patients with a total of 34 [⁶⁸Ga]Ga-DOTATATE PET/CT and 113 [⁶⁸Ga]Ga-DOTATOC PET/CT scans. An abnormal UP uptake was seen in 32 patients with 65.7% of suspicious NET lesion or extrinsic compression on morphological imaging. Normal UP uptake SUV_max/mean were measured in 115 [⁶⁸Ga]Ga-SST scans (78.2%) with normal UP uptake and without suspicious lesion on morphological imaging. We found an average SUV_max of 12.3 ± 4.1 for [⁶⁸Ga]Ga-DOTATATE and 19.8 ± 9.8 g/ml for [⁶⁸Ga]Ga-DOTATOC, hence higher than those reported in the literature [SUVmax 5 ± 1.6 to 12.6 ± 2.2 g/ml] with significant difference with abnormal UP uptake and between both PET tracers (both p < 0.01). Significant results were a higher UP uptake on [⁶⁸Ga]Ga-DOTATOC in male patients (p = 0.02) and significant associations between UP uptake on [⁶⁸Ga]Ga-DOTATOC and SUV_max/mean of the primary tumor (ρ [0.337-0.363]; p [0.01-0.02]).

Conclusion: We confirmed a higher and very frequent UP uptake in latest SiPM-detector [⁶⁸Ga]Ga-SST PET/CT with an even higher uptake in patients that had [⁶⁸Ga]Ga-DOTATOC PET/CT. SUV_mean/max were significantly higher in abnormal UP uptake but there were overlaps with UP SUV values for both [⁶⁸Ga]Ga-SST and a correlation to morphological imaging is crucial. Besides, significant associations between UP uptake and SUV_mean/max of the primary NET as well as patients' gender were seen in the larger cohort of [⁶⁸Ga]Ga-DOTATOC patients suggesting that both physiological and pathological parameters could affect UP uptake.